Structural Behavior of Asphalt Pavements

1045 Pages·2016·53.295 MB·English

by  Lijun Sun

Structural Behavior of
Asphalt Pavements
Structural Behavior of
Asphalt Pavements
Lijun Sun
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Preface
When current knowledge could not explain the questions we are facing, we prefer
following our inner feeling to insight and grasp the beautiful essence in pavement
world, and trying to shape them into science level, rather than defend tenaciously
thosefragmented experience knowledge although those were classical.
Since 1991, myresearch interests have transferred partially from the pavement
managementareatotheasphaltpavementarea.Inthattime,theresearchonasphalt
pavementhashadalonghistoryandmadebrilliantachievementsintheworld.Butin
China,theresearchhistoryonasphaltpavementwasnotverylong,andtheengineer-
ingexperienceswerenotsorich.ThisiswhyIdecidedtoselecttheasphaltpavement
as mylong-term research area.
WiththefreewayformingawholenetworkinChina,thetrafficvolumeandaxle
loadmagnitudehasincreasedsharply.Thenationalaveragepercentageoftruckson
the freeway is 40%, and the heavy weight of these vehicles causes a very serious
prematuredistressofthepavement.Overmorethantwodecades,manynewpave-
ment techniques, such as modified asphalt, SMA, Superpave, long-life pavement,
andhigh-modulusasphalt,wereintroducedintoChinasopromptlythatthedevelop-
ment of the pavement techniques seemed to be booming. Additionally, a large
amount of research on asphalt pavement structure and material were conducted
throughout the world in order to face up to the challenges from the heavy load of
vehicles. Some researchers madegreateffortsto integrate the fragmentation pave-
mentresearchresultsintoacomprehensivetheoryforpavementanalysisanddesign,
buttheeffectivenessofthispracticedoesnotlookassignificantasexpected.These
researchresultsareconsideredtobethesimpleextrapolationofconventionaltheo-
riesandmethodsforlight-dutypavement,whichiswellsuitedfortheanalysisand
designofconventionalasphaltmixture,butnotforemergingmaterials.Theseresults
cannotreflecttheperformanceofpavement,norcantheygiveaclearguidetopave-
mentcomponentdesign;thereforetheyareconsideredonlylittlehelpinsolvingthe
problems of very heavy-duty pavement structures. We face a number of questions
and challenges, including: how to effectively solve pavement problems due to
extremelyheavyloads;howtoconsideremergingmaterialsandtechniquesinpave-
mentdesign;andhowtointegratethenewtechniques,newmaterials,andnewcon-
cept togetherfor success.
Withthisinmind,westartedourpavementresearch.Infact,theaforementioned
challengesbecamethedriveforustoadheretoasphaltpavementformorethantwo
decades.Thepavementworldissocomplicatedthatwecannotseethedirectionahead.
Butinthevastmistthereisalwaysaflickeringdimlightleadingustopursue,notsee
thetruth,hardtoshakeoff.Overtheyears,theencouragesfromsomepredecessors
excitedouroftenlanguorousspirit,thedoubtandcontroversyfromsomecolleagues
helpedusimproveourresearches.Thesuccessfulapplicationoftheresearchresults
demonstratedthevalueoffundamentalresearchinpavementstodecisionmakers,who
thengaveusfinancialsupporttocontinue.Theprocessofrethinking,restructuring,
xvii
xviii Preface
andrefiningasphaltpavementhelpedusoptimizenewunderstandingofthepavement
problems. By the end of 2001, we had finished the first stage in our research of
pavementbehavior,andby2005,wehadformedaclearframeworkontheasphalt
pavementbehavior.Sincethen,wehavesupplementedtheresearchonthepavement
deformation,whichnowformstoday’spavementbehaviordynamics.
Thepublicationofthisbookmeansthatthepavementresearchwebeganin1991is
now coming to an end. The “new students” who participated in this early round of
researchinmygrouparenowthe“seniorexperts”intheChinesehighwayfield.With
overtwodecadesofresearch,wecametorealizethebehavioralcharacteristicsofthe
asphalt pavement structure and the limits of mechanistic analysis. The asphalt
pavementissocomplexthatthemodernmechanistictheorycanonlyhelpqualitatively
analyze the known phenomenon, but it cannot accurately reflect the complicated
performanceofasphaltpavementstructureandmaterials.Therefore,itisdifficultto
discoverunknownlawsforasphaltpavement,asanyguideavailableisverylimited
inpractice.Thismaybethebasicreasonthatempiricalanalysisanddesignstillplay
dominant roles in pavement practice. In order to understand the accurate behavior
characteristicsofasphaltpavement,itisnecessarytodevelopanewroadmap,based
onwhichtheintegrationoftheoreticalanalysis,testresult,andengineeringexperience.
Inordertobetterunderstandthebehavioralcharacteristicsofasphaltpavement,
more accurate and finer theoretical analysis and tests on pavement structure and
materialshavebeenconductedthroughouttheworld.Afteranalyzingtheimpressive
amountofresults,wefoundthatthescaleeffects(ie,continuityaspects)inthefine
analysisandtestingbecomesmoreandmoresignificant.Whenthepavementiscon-
sideredtobeastructurewhichisconsistedofcontinuummaterials,wecanmakean
integralresponseanalysisofpavementfromthemacroscopicpointofview,whilethe
commonlyused strain/stress isamicroscopic indicator,which isinfluencedby the
inherentparticleeffects(granulareffects)ofpavementmaterials.Thisistosaythat
pavementmaterialsexhibitsignificant“particleeffects,”(ie,granulareffects).Inthe
caseoflighttrafficload,theintegrityofpavementmaterialsplaysadominantrole,
butinthecaseofheavytrafficload,especiallyinthecaseofhightemperature,the
particleeffectofpavementmaterialscannotbeignored.Inthepavementanalysis,it
isdifficulttobalancetheintegrityandparticleeffectsinaconventionalcontinuum
mechanistic whether using the elastic or viscoelastic theory. The discrete element
method permits the analysis of the interaction between the particles of materials,
butitisstillfarfromthemacroscopicperformanceofpavement.Inordertobridge
thegapbetweenthemicroscopicanalysisandmacroscopicperformance,itisneeded
todevelopanewindicator,newmethod,ornewtheoryinwhichthemechanisticcan
begivenwiththerightroles.Here,anewguidelineforpavementresearch,“quali-
tativeresearchmustbecorrect,quantitativeresultshouldbereasonable,”isputfor-
ward,anda“BridgePrinciple,”whichcanbridgesthegapbetweenthemicroscopic
behaviorandmacroscopicperformance,isestablishedasanewmethodologyinthis
book.ThroughtheBridgePrinciple,theparticleeffectsofmaterialsareeffectively
avoided.IntheBridgePrinciple,theanalysisanddesignparametersinpavementare
re-explainedtobethecriticalvariablesasabridge,notarealresponseofpavement.
Then,inconjunctionwiththetestedand/orobservedresults,thereasonablyquanti-
fiedresultsweregiven.Thisprocessmeansthatthemechanisticasarationalanalysis
Preface xix
method may be a better tool at abstracting, refining, and transplanting successful
experiencethanasadirectdesigntool,therebydemonstratinganewresearchroad-
map.With this roadmap, we conceive the logic frameworkin which the pavement
performanceandmechanisticresponseareincorporatedtogether,aswellasdeduce
the intrinsic consistency relations between the macroscopic (performance) and the
microscopic(mechanisticresponse),structure,andmaterial,aswellastheintegrity
and the particle.
Ourunderstandingonasphaltpavementcamefromtheresearchpractice,andgave
theguidebacktoourresearchpracticeintime.Throughtheresearchofthepastmore
thantwodecades,wedefinedthedistressmechanismfortheheavy-dutypavement
andputforwardthe“two-waycontrol”pavementdesignrule.Therulechangesthe
conventionalwayforpavementcomponentdesignandensurestheintegralbalance
of resistance between pavement structure layers. We accumulated a large amount
of first-hand data for the pavement performance, based on which put forward
thedeteriorationlawofpavementperformance,andestablishedthepavementbehav-
iorequation.WepresentedtheBridgePrinciple,whichunifiesthepavementbehavior
equation and the pavement fatigue equation, proving that the pavement fatigue
equation is a special case of the pavement behavior equation. We believe that
theBridgePrincipleprovidesafeasibleroadmaptotransfertheresultswithvarious
scalecharacteristics.BasedontheBridgePrinciple,werealizedthetransferfromtest
resultsinlaboratorytorealpavementperformance.Throughintroducingadimension-
less variable to avoid the particle effects, we developed the deformation analysis
equation.Thepavementbehaviorequation,pavementfatigueequation,anddeforma-
tionequationformstheentiresystemwithanintrinsicconsistency,whichwecallthe
pavementbehaviorequation’sgroup.Thisistosaythatonerule,oneprinciple,and
one equation group represents the core of new pavement theory developed in this
book.Thesearethefruitsofthejointeffortsofallresearchers.
Thecontentinthebookfinishedindifferenttime,theresearchprocessandresults
inthattimearepersisted.LijunSunisresponsibleforalltheresearchofthepavement
issuesdescribedinthisbook,aswellastheoutlinesetofthebookandthewritingof
Chapters1,5(Section5.6),8(Section8.1),10,11.2(Section11.2),and14,aswellas
thefinalizationofallchaptersinmanuscript.Otherresearchparticipantsandwriters
are shownin followingtable.
Writerin Writerin
ChapterNumbers ResearchParticipants Chinese English
1 LijunSun LijunSun
2 JianQin JianQin LuJia
LuJia LijunSun
XinyiZhengandLiping
Liu
JianliangWu
Continued
xx Preface
Writerin Writerin
ChapterNumbers ResearchParticipants Chinese English
3 XiaodiHu XiaodiHu XiaodiHu
FengLI
4 HongchaoZhang HongchaoZhang HongchaoZhang
XiaodiHu
QunleDu
5 5.1–5.5 HongchaoZhang HongchaoZhang HongchaoZhang
5.6 HongchaoZhang LijunSun HongchaoZhang
5.7–5.9 YufengBi LijunSun LijunSun
GangWang
HongchaoZhang
6 XipingLiu LipingLiu LuJia
ZhijunXu
ZijianChen
FangyanLuo
LipingLiu
7 LipingLiu LipingLiu XiaoyangJia
8 8.1 LipingLiu LijunSun XiaoyangJia
8.2–8.5 LipingLiu
9 ZhenglanLu KaiSu KaiSu
KaiSu
LipingLiu
WenTang
10 10.1–10.4 LijunSun LijunSun LijunSun
10.5 ChunhuaHu
10.6 LipingLiu
11 11.1,11.3– YufengBi YufengBi JingnaZhang
11.6 PengCui
11.2 LipingLiu LijunSun
12 YiWang LipingLiu KaiSu
LipingLiu
YanXu
GangWang
13 JingnaZhang YongPeng YongPeng
YuliangYang
YongPeng
14 LijunSun LijunSun LijunSun
We appreciate all colleagues who supported our pavement research. We also give
many thanks tothe editorsof Elsevierfor their help.
Lijun Sun
School ofTransportation Engineering,TongjiUniversity
August 2015
CHAPTER
1
Introduction
1.1 PAVEMENT DESIGN REQUIREMENTS
Pavement structure isa part of road structure, which consists of the following ele-
ments:subgrade,subbasecourse,basecourse,andasphaltlayer,allofwhichdirectly
beartheeffectsofheavyloadsandenvironmentalconditions.Thebasicrequirements
forpavementaredurability,smoothness,andsafety(ie,skidresistance).Pavement
should also be constructed in a way that is as friendly to environment as possible.
Durability means longer service life; that is, the pavement structure must have
enough strength and resistance todeformation. Infact, all ofthe current pavement
designmethodswereestablishedbasedondurability,whichisthecoreofpavement
design.Thesmoothnessofpavementensuresridingcomfort,whichismoreimpor-
tantfordriversonfreewaysandhighwaysbecauseoffastertravelspeeds.Ifthepave-
mentissmooth,itnotonlyensuresahighqualityofriding,butitalsodiminishesthe
potentialdamageduetothedynamicloadsofvehiclestopavements.Asaresult,the
pavementwilllastlonger.Inordertoensureapavement’ssmoothness,properstruc-
ture,materialdesign,andconstructionarenecessary.Skidresistanceistherequire-
menttothesurfacecharacteristicsofpavement,meansthedrivingsafetyprovidedby
the pavement wearing course,traditionally notincludedin the structure design.
A pavement can become distressed in various ways, including cracking
(eg,fatiguecracking,low-temperaturecracking,andreflectivecracking),deforma-
tion and new emerging distresses. When pavement becomes distressed early on, it
meansthatitwasconstructedwithinadequatedurability.Toomuchdistressmeans
thepavementisnolongerusable;therefore,itissaidtohaveashortlifespan.Thisis
why limitingand delaying distress are the main objectives in pavement design.
When compared with other structures of highway engineering, the lifespan of
pavementstructureisveryshort.Generally,thedesignlifetimefortheasphaltpave-
mentsisonly15yearsinChinatosavetheinitialconstructioncost.Withincreasing
trafficvolume,theeffectsofpavementmaintenanceandrehabilitationonthehigh-
way traffic become more and more significant, so the design lifetime of pavement
tendstobe longer,which gradually evolved into the long-life pavement concept.
Themissionofpavementdesignistoinsurepavementwithoutunacceptabledis-
tresswithinpavementdesignlifeperiod.Inordertorealizethisobjective,thevarious
factors,suchaspavementstructure,material,load,environmentandeconomy,etc.,
mustbeconsideredcomprehensively,withthefinalcriterionbeingtheperformance
ofpavement.Thereforewhatthepavementdesignisbasedontheperformanceisa
1
StructuralBehaviorofAsphaltPavements.http://dx.doi.org/10.1016/B978-0-12-849908-5.00001-8
#2016ElsevierInc.Allrightsreserved.
2 CHAPTER 1 Introduction
reasonablechoicewhenyouconceivethepavementdesignconcept.Thisisnotonly
a trend ofthe development, also aconsequence of the development.
Subsequently,anumberoftherepresentativepavementdesignmethodswillbe
discussed inrelationtohow they meet the requirements ofpavement design.
1.2 REPRESENTATIVE PAVEMENT DESIGN METHODS
1.2.1 EMPIRICAL-BASED DESIGN METHODS
1.2.1.1 California bearing ratio design method [1,2]
TheCaliforniabearingratio(CBR)isanindicatorthatdescribesthecharacteristics
ofpavementmaterialsdevelopedinthe1920sbytheUSCaliforniaDivisionofHigh-
way.CBRexpressestheratioofthepenetrationresistancebetweenthetestmaterial
andthestandardgranular.Themeanwhileinvestigationshowsthatthedominantdis-
tress types of pavements are the lateral displacement of subgrade material due to
absorbingwater,thedifferentialsettlementofmaterialsbeneaththepavementlayer,
and too much pavement deflection. Based on the investigation results, the CBR
designmethod andthedesigncurvessuited forthe California’strafficandclimate
conditions were developedto control the shear distressof the subgrade.
In the early part of World War II, the comprehensive investigation of flexible
pavement design methods was made by the US Army Corps of Engineers, which
ledtoCBRbeingselectedasthedesignmethodofchoicefortherunwaypavements.
Duetoalargeloaddifference,theCBRtestprocedurewasmodified,andthethick-
nessdesigncurvedevelopedforhighwayloadwasextendedtoaccommodatearange
inaircraftwheelloadsbasedontheshearequivalence.Inthebasisofmanyyearsof
research and practice, the formula of the pavement thickness, wheel load, and tire
pressure was presented in 1956 and was then modified according to the effects of
repeated loads and heavy loads. As a result of this development, the equivalent
single-wheel load concept was introduced.
InthebasisoftheCBRdesignprocedureoftheUSArmyCorpsofEngineers,the
USGranularAssociationdevelopedtheCBRdesignmethodforhighwaypavements
in1972.TheguidelineoftheCBRmethodisthatthepavementdesignshouldpro-
vides adequate thickness and quality to prevent any pavement layer from repeated
shear deformation and frost effects.
TheCBRdesignmethodisanempiricalmethodwithaclearconceptandsimple
procedure,makingitsuitableforthethicknessofthedesignneededforheavy-duty
pavement.
1.2.1.2 AASHTO design method [3,4]
AASHO (present AASHTO, American Association of States Highway and Trans-
portationOfficials)pavementdesignmethodgrowsoutofAASHORoadTestscon-
ducted during 1958–62. It is a design method that had and continues to have
significant influence. The Road Test was finished by the end of 1961, and the
researchsummaryreports were presentedinMay 1962,which consistedofalarge
1.2 Representative pavement design methods 3
amountofvaluabletestdataregardingthepavement’sdesign,construction,andper-
formance.Basedontheresearch,AASHOInterimGuidefortheDesignofFlexible
Pavementswaspublishedin1961,andAASHOInterimDesignGuideforDesignof
Pavement Structures was published in 1972. Then, the revised AASHTO Design
Guide was formallyissuedin 1986and 1993 respectively.
In AASHO (AASHTO) design method, the present serviceability index (PSI)
conceptwasputforwardtoreflecttheservicelevelofpavement.Throughthesub-
jectiveratingoftheservicelevelandtheobjectivemeasurementofpavementcon-
ditionsofthesameroad,therelationshipbetweenPSIandpavementconditionswas
developed,asshowninEq.(1.1).Therating(0–5inscale)ofthepavementwascon-
ductedbyrating’spanel,whileobjectivemeasurementsincludetheslopechangeof
pavement surface, ruttingdepth, andcracking areas.
(cid:1) (cid:3) (cid:5)pffiffiffiffiffiffiffiffiffiffiffi(cid:6)
PSI¼5:03(cid:2)1:91lg 1+SV (cid:2)1:38RD2(cid:2)0:01 C+P (1.1)
where
PSI isthe present serviceability index.
SV isthe average change of slope.
RD isthe average rutting depth (cm).
Cisthe map-cracking area per 1000ft2 pavement (m2).
P isthe patching area (m2).
The initial basic design equation ofthe designmethod is:
ΔPSI
lg
lgW ¼9:36lgðSN+1Þ(cid:2)0:2+ 4:2(cid:2)1:5 (1.2)
18 1094
0:40+
ðSN+1Þ5:19
where
W isthe cumulated number ofESAL (equivalent single axle load)(18kips)
18
over the design lifetime of pavement.
ΔPSI isthe difference between initial PSI and terminal PSI (4.2(cid:2)PSI),which
t
depends onthe highway grade.
SN isthe structure number ofpavement, which describes the total equivalent
thicknessof pavement structure, as shown inEq. (1.3):
SN¼a D +a D +a D (1.3)
1 1 2 2 3 3
where
a isthe materialcoefficient ofith layer.
i
D isthe thicknessof ithlayer(in.).
i
Thestructurenumber(SN)ofpavementisspecificallydefinedintheAASHOmethod,
which expresses the total resistance of the pavement structure except the subgrade.